Postmortem Changes in Fish

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Questions and Answers

The first sensory changes in fish during storage primarily involve changes in texture and odour.

False

Rigor mortis in fish begins immediately after death when the muscles are completely relaxed.

True

The onset of rigor mortis is uniform across all fish species regardless of handling and temperature.

False

High temperatures consistently accelerate the onset of rigor mortis in tropical fish.

False Signup and view all the answers

Once rigor mortis resolves, the muscle becomes elastic again and retains its original firmness.

False Signup and view all the answers

Glycogen reserves in fish have no effect on the timing of rigor mortis onset.

False Signup and view all the answers

Handling methods used for stunning fish have no impact on the onset of rigor mortis.

False Signup and view all the answers

Temperature differences between sea and storage conditions affect the time from death to rigor onset in carp.

True Signup and view all the answers

Killing a fish by stunning results in the fastest onset of rigor mortis.

True Signup and view all the answers

Cooking a fish pre-rigor results in a tough and dry texture.

False Signup and view all the answers

White muscle in fish may shrink up to 52% of its original length during rigor.

False Signup and view all the answers

Filleting a fish in rigor results in poor filleting yield due to stiffness.

True Signup and view all the answers

The time from death to the end of rigor for unstressed cod at 0°C can last up to 96 hours.

True Signup and view all the answers

Fish stored in ice spoil less rapidly than fish stored under chilled conditions without ice.

True Signup and view all the answers

Sensory evaluation of fish does not depend on the storage method used.

False Signup and view all the answers

During phase 3 of fish deterioration, the flesh can develop a sickly sweet smell.

True Signup and view all the answers

Trimethylamine (TMA) is produced from the bacterial reduction of trimethyl-aminoxide (TMAO) in spoiled fish.

True Signup and view all the answers

The characteristics of freshness in fish can vary based on the species and storage conditions.

True Signup and view all the answers

Fish spoilage occurs primarily due to autolysis and microbial activity.

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The highest quality of fish is indicated by a sensory evaluation score of 10.

True Signup and view all the answers

ATP production in fish muscle tissue continues normally after death.

False Signup and view all the answers

Enzymatic spoilage in fish happens after microbial spoilage.

False Signup and view all the answers

Cod's pH drops from 6.8 to a range lower than 6.0 during post-mortem glycolysis.

False Signup and view all the answers

Fish display bright, iridescent pigmentation when they are spoiled.

False Signup and view all the answers

Anaerobic conditions are sufficient for muscle energy production in living teleost fish.

False Signup and view all the answers

The sensory evaluation scale for fish ranges from 0 to 10, with the rejection level set at 4.

True Signup and view all the answers

Opaque mucus on fish gills indicates a high quality of fish.

False Signup and view all the answers

Octopine is the end-product from the anaerobic metabolism of cephalopods.

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Soft and flaccid fish flesh indicates high freshness.

False Signup and view all the answers

Fish flesh should be bluish and translucent for it to be considered fresh.

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The production of energy in post-mortem muscle is solely aerobic.

False Signup and view all the answers

The coloration of fish organs such as kidneys should remain bright red when the fish is fresh.

True Signup and view all the answers

Collagenase enzymes are believed to originate from the muscles of prawns.

False Signup and view all the answers

The enzyme TMAO-ase is responsible for converting TMAO into dimethylamine and formaldehyde.

True Signup and view all the answers

The removal of the kidney is not crucial for minimizing toughening in gadoid fish during frozen storage.

False Signup and view all the answers

The ultimate rigor pH in large mackerel can be as low as 5.8-6.0.

True Signup and view all the answers

Physical abuse to fish before freezing can accelerate the production of formaldehyde.

True Signup and view all the answers

Storing fish at a temperature of less than -30°C helps prevent the autolytic production of formaldehyde.

True Signup and view all the answers

Fish muscle typically contains a higher level of glycogen than mammalian muscle.

False Signup and view all the answers

Rigor mortis results in a decrease in muscle ATP levels below 1.0 µmoles/g.

True Signup and view all the answers

The enzymatic activity of TMAO demethylase is higher in white muscle compared to red muscle.

False Signup and view all the answers

Temperature fluctuations during frozen storage have no effect on the level of formaldehyde produced.

False Signup and view all the answers

Bleeding of fish has no effect on the post mortem production of lactic acid.

False Signup and view all the answers

Autolysis in fish can lead to a gradual production of bitterness due to breakdown of ATP.

True Signup and view all the answers

The K value is a freshness index based on the degradation of ATP-related compounds in fish muscle.

True Signup and view all the answers

Removing calcium can prevent the activation of calpain, which is involved in muscle softening.

True Signup and view all the answers

ATP is solely responsible for muscle contraction in fish.

False Signup and view all the answers

Glycolytic enzymes are responsible for the production of lactic acid, resulting in a decrease in the pH of fish tissue.

True Signup and view all the answers

A fish in rigor mortis becomes too stiff to be filleted or processed easily.

True Signup and view all the answers

The relationship between muscle toughness and pH is direct; higher pH levels lead to increased toughness.

False Signup and view all the answers

Sodium chloride has a strong inhibitory effect on enzyme activity.

True Signup and view all the answers

Cathepsin D is primarily responsible for the softening of salmon muscle during spawning migration.

False Signup and view all the answers

Chiba et al. (1991) found that non-struggling fish have a greater pH drop compared to struggling fish.

False Signup and view all the answers

Freezing and thawing fish tissue enhances autolytic activity of membrane-bound enzymes.

True Signup and view all the answers

The degradation of ATP catabolites progresses at the same rate across all fish species.

False Signup and view all the answers

Calpains require high concentrations of calcium to be activated.

True Signup and view all the answers

IMP is associated with a desirable fresh fish flavor.

True Signup and view all the answers

Calpains in fish and crustaceans have similar digestive capabilities.

False Signup and view all the answers

Loss of water in fish muscle during cooking is beneficial for its texture.

False Signup and view all the answers

Stressing fish before capture leads to an increase in glycogen stores.

False Signup and view all the answers

Collagenases are responsible for the breakdown of myocytes during chilled storage.

True Signup and view all the answers

The breaking strength of fish muscle is negatively correlated with cathepsin L activity.

False Signup and view all the answers

The softening of muscle during resolution of rigor is a completely understood process.

False Signup and view all the answers

Postmortem changes in freshness are solely indicated by the degradation of nucleotide catabolites.

False Signup and view all the answers

Type V collagen solubilization leads to increased instrumental measurements of fish muscle texture.

False Signup and view all the answers

Molecular weight of myosin heavy chain fragments formed by fish calpains is approximately 150,000 Da.

True Signup and view all the answers

Cathepsins are responsible for detrimental changes in texture for fermented fish products.

True Signup and view all the answers

Tropical fish are more susceptible to calpain autolysis than fish adapted to colder temperatures.

False Signup and view all the answers

The activity of calpains is maximized at high pH levels.

False Signup and view all the answers

Proteolytic enzymes secreted by parasites have been conclusively identified in infected fish muscle.

False Signup and view all the answers

The rates of formation and breakdown of IMP were the same in both sterile and non-sterile samples of cod tissue.

True Signup and view all the answers

Bacterial nucleoside phosphorylase has no impact on the conversion of Iino to Hex.

False Signup and view all the answers

The breakdown rate of nucleotide catabolites is greater in non-sterile fillets than in sterile fillets.

False Signup and view all the answers

The presence of autolytic enzymes is enhanced when fish are physically handled.

True Signup and view all the answers

Surette et al. were able to recover nucleoside phosphorylase from freshly killed cod.

False Signup and view all the answers

Belly-bursting in pelagic fish is primarily influenced by biological factors such as fish size and feed content.

False Signup and view all the answers

Cathepsins are a type of proteolytic enzyme that remains inactive in living tissue.

True Signup and view all the answers

The breakdown of proteins through autolysis can lower the nutritional value of fish.

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Autolytic changes cause significant softening of fish tissues primarily due to nucleoside phosphorylase activity.

False Signup and view all the answers

The conversion of inosine to hypoxanthine is inferred to be useful for determining freshness in various fish species.

False Signup and view all the answers

Proteolytic breakdown in fish muscle leads to the production of low molecular weight peptides.

True Signup and view all the answers

Fish should be stored in deeper boxes for optimal preservation and to minimize autolysis.

False Signup and view all the answers

Freezing and thawing processes have minimal effect on the autolysis of fish tissue.

False Signup and view all the answers

What occurs during the resolution of rigor mortis in fish?

Muscle relaxes but remains less elastic than before. Signup and view all the answers

How does the temperature influence rigor mortis in cod fish?

High temperatures cause a rapid onset and strong rigor mortis. Signup and view all the answers

What effect do starved fish have on the rigor mortis onset?

Starved fish experience an immediate onset of rigor mortis. Signup and view all the answers

Which statement accurately describes the relationship between handling methods and rigor mortis onset?

Some handling methods can accelerate the onset of rigor mortis. Signup and view all the answers

How does the difference between sea temperature and storage temperature affect rigor mortis in carp?

A larger temperature difference results in a shorter time to rigor onset. Signup and view all the answers

What is the primary consequence of strong rigor tensions in cod fish?

Rupture of the fillet due to gaping. Signup and view all the answers

What sensory element is NOT typically used to evaluate the freshness of fish?

Weight Signup and view all the answers

Which factor might inhibit the rate of rigor mortis onset in fish?

High levels of glycogen. Signup and view all the answers

What is the impact of cooking fish that is still in rigor mortis?

The texture is tough but not dry. Signup and view all the answers

How long can the onset of rigor mortis take for unstressed cod at 0°C?

14-15 hours Signup and view all the answers

Which of the following contributes to the poor filleting yield when a fish is filleted in rigor?

The fish body is completely stiff. Signup and view all the answers

What characterizes the flesh of fish post-rigor?

It is firm, succulent, and elastic. Signup and view all the answers

Which factor is most crucial for maintaining fish quality during frozen storage?

Careful thawing at low temperatures. Signup and view all the answers

What sensory change occurs during phase 3 of fish deterioration?

The flesh develops off-flavours. Signup and view all the answers

Which statement about handling methods affecting rigor mortis is accurate?

Stunning always results in a quick onset of rigor mortis. Signup and view all the answers

During which phase is fish characterized by a neutral taste and no off-flavours?

Phase 2 Signup and view all the answers

What happens to dark muscle when stored post-mortem?

It may shrink up to 52% of its original length. Signup and view all the answers

What is indicated by a sensory evaluation score of 3 in fish quality assessment?

Best quality. Signup and view all the answers

What characteristic indicates the highest quality in fish appearance?

Bright, iridescent pigmentation and no discoloration Signup and view all the answers

Which condition of fish flesh is indicative of spoilage?

Velvety, waxy, and dull Signup and view all the answers

What happens to the color of fish kidneys and blood after spoilage?

They turn completely brownish Signup and view all the answers

How does the pH of cod muscle change during post-mortem glycolysis?

It drops to 6.1-6.5 Signup and view all the answers

What is characterized by the accumulation of lactic acid and a drop in tissue pH?

Post mortem glycolysis Signup and view all the answers

What does the sensory evaluation scale for fish indicate when the score is set at 4?

Rejection level Signup and view all the answers

What occurs immediately after a fish dies regarding muscle energy production?

Anaerobic respiration takes over Signup and view all the answers

Which type of spoilage occurs predominantly in certain fish species like squid and herring?

Enzymatic spoilage Signup and view all the answers

What is the primary consequence of ATP depletion in fish muscle post-mortem?

Onset of rigor mortis Signup and view all the answers

Which of the following statements about tissue condition after spoilage is false?

Muscle maintains its original firmness Signup and view all the answers

What indicates a good sensory evaluation score for fish?

8-10 Signup and view all the answers

How does temperature affect the rate of rigor mortis onset in fish?

Higher temperatures accelerate rigor mortis onset Signup and view all the answers

How does a fish's condition change immediately after death?

It enters a state of rigor mortis Signup and view all the answers

The production of energy in fish muscle post-mortem relies primarily on which process?

Anaerobic glycolysis Signup and view all the answers

What primarily accelerates the conversion of Iino to Hex in non-sterile cod samples?

Presence of nucleoside phosphorylase Signup and view all the answers

What effect does physical handling have on chilled fish?

It enhances bacterial spoilage Signup and view all the answers

What enzyme is believed to be significantly involved in the autolytic degradation of fish tissue?

Cathepsins Signup and view all the answers

How do variations in Hx levels among different fish species affect their freshness determination?

Hx determination may not be useful for certain species. Signup and view all the answers

What is a major consequence of belly-bursting in pelagic fish species?

Lower commercial acceptability Signup and view all the answers

What is the role of cathepsins in living fish tissue?

They remain inactive within lysosomes. Signup and view all the answers

Which practice is crucial for minimizing autolytic processes during fish storage?

Limiting storage box depth to 30 cm Signup and view all the answers

In the context of autolysis, what happens to the tissue of bulk-stored capelin?

It speeds up the growth of spoilage bacteria. Signup and view all the answers

What impact does the freezing/thawing cycle have on herring compared to biological factors?

It influences belly-bursting more than biological factors. Signup and view all the answers

What might occur when nucleoside phosphorylase is not recovered from freshly killed cod?

There is a delay in the production of Hx. Signup and view all the answers

What effect do low molecular weight peptides have on fish muscle after autolysis?

They contribute to texture softening. Signup and view all the answers

What storage practice is recommended for maintaining the quality of iced fish?

Avoiding any physical damage Signup and view all the answers

What is a significant characteristic of autolytic enzymes in fish tissues?

They can be compartmentalized. Signup and view all the answers

What is the primary factor affecting the amount of lactic acid produced in fish muscle after death?

The initial level of glycogen in the fish Signup and view all the answers

Which fish species is mentioned as having an ultimate rigor pH as low as 5.4-5.6?

Tuna Signup and view all the answers

What effect does bleeding fish have on lactic acid production post mortem?

It reduces lactic acid production Signup and view all the answers

What happens to the net surface charge of muscle proteins as the pH drops in fish muscle?

It decreases, leading to partial denaturation Signup and view all the answers

What is the primary consequence of the action of collagenase enzymes in chilled prawns?

Softening of the tissue Signup and view all the answers

Which organ is thought to be the source of collagenase enzymes in prawns?

Hepatopancreas Signup and view all the answers

During autolysis, what happens to ATP levels in fish muscle after death?

They degrade in a predictable manner Signup and view all the answers

What is the relationship between muscle toughness and pH in fish as indicated in the content?

Muscle toughness decreases with higher pH levels Signup and view all the answers

What is the role of the enzyme TMAO-ase in fish tissue?

Conversion of TMAO to DMA and formaldehyde Signup and view all the answers

Which ATP degradation product is responsible for the desirable fresh fish flavor?

Inosine monophosphate (IMP) Signup and view all the answers

Which muscle type has a higher rate of TMAO demethylase activity?

Red muscle Signup and view all the answers

What effect does formaldehyde have on fish muscle when produced during storage?

Induces cross-linking of muscle proteins Signup and view all the answers

What occurs to fish muscle that is in rigor mortis regarding its physical handling?

It becomes too stiff to be easily filleted Signup and view all the answers

What storage condition is recommended to minimize the production of formaldehyde in fish?

Temperatures less than -30°C Signup and view all the answers

What conclusion can be drawn about the K value in relation to fish freshness?

Some species show a maximum K value before reaching shelf life Signup and view all the answers

What is a significant effect of rough handling of fish prior to freezing?

Increased formaldehyde production Signup and view all the answers

What role does calcium play in muscle contraction in fish?

It activates ATP-ase and reduces free ATP levels Signup and view all the answers

How does pre-capture stress affect the pH of fish muscle over time?

It results in a larger drop in pH compared to non-stressed fish Signup and view all the answers

Which autolytic change leads to a loss of fresh fish flavor?

Breakdown of ATP Signup and view all the answers

What is a recommended practice to avoid toughening of minced fish during frozen storage?

Removing all organ tissues Signup and view all the answers

Which enzyme is involved in the significant softening of muscle tissue during the resolution of rigor?

Calpain Signup and view all the answers

What is the relationship between temperature fluctuations during storage and formaldehyde production?

Fluctuations increase formaldehyde production Signup and view all the answers

Why is ATP considered important for muscle contraction in living fish, aside from providing energy?

It acts as a muscle plasticizer Signup and view all the answers

How does muscle tissue in rigor mortis respond to heating during cooking?

It loses moisture and becomes tougher Signup and view all the answers

What effect does the presence of 5% sodium chloride have on the enzyme activity of Reddi's enzyme?

Enzyme activity is completely inhibited. Signup and view all the answers

Which cathepsin is primarily implicated in the softening of salmon muscle during spawning migration?

Cathepsin L Signup and view all the answers

What property of cathepsin L was demonstrated to correlate with muscle texture in salmon?

Autolytic activity Signup and view all the answers

How do calpains differ from cathepsins regarding their activity in fish muscle?

Calpains digest myofibrillar proteins more specifically. Signup and view all the answers

What role do calpains play in the texture of fish muscle during storage?

They contribute to autolysis. Signup and view all the answers

What is one consequence of freezing and thawing fish muscle regarding enzyme activity?

Increased autolytic enzyme reactivity. Signup and view all the answers

What factor greatly influences calpain activity in fish species?

Environmental temperatures Signup and view all the answers

What is the primary substrate that calpains digest in vertebrate muscle?

Tropinin-T Signup and view all the answers

What is a notable effect of collagenase enzymes during fish storage?

Cause gaping in muscle tissue. Signup and view all the answers

What happens to the type V collagen in chilled trout muscle over time?

It becomes solubilized, reducing texture. Signup and view all the answers

At which temperature does gaping become inevitable in Atlantic cod?

17°C Signup and view all the answers

What is the primary function of the myocommata in teleost fish?

Division of muscle cells into flakes. Signup and view all the answers

How does the enzymatic activity of calpains in fish compare to that in mammals?

Higher activity in fish at low temperatures. Signup and view all the answers

What condition influences the cleavage rate of myosin by fish calpains?

Heat stability. Signup and view all the answers

Study Notes

Postmortem Changes in Fish

Sensory Changes

Sensory changes include alterations in appearance, odor, texture, and taste during fish storage.
Initial changes involve loss of characteristic taste, developing within the first few days in ice.
Rigor mortis sets in post-mortem, transitioning fish muscle from a relaxed state to a stiff, inflexible condition.
Onset and resolution of rigor mortis depend on species, temperature, handling, and fish size.
For cod, high temperatures accelerate rigor mortis, while in tropical fish, a colder temperature may expedite rigor onset.
Pre-rigor filleting retains better texture and yield compared to post-rigor.
Consumption texture differs notably between pre-rigor (soft) and post-rigor (tough but moist) fish.
Sensory evaluation of raw fish includes assessing appearance, texture, and odor, affected by storage method (iced vs. chilled).
Fish stored under different methods exhibit varying levels of quality and spoilage indicators utilizing a scoring system (0 to 3 for raw quality).

Autolytic Changes

Autolysis refers to self-digestion processes influenced by enzymatic and microbial activity in fish spoilage.
Enzymatic changes can happen independently of bacterial spoilage initial stages and predominate in some species.
The interruption of oxygen supply after death leads to anaerobic respiration, restricting energy production in muscle tissues.
Limited ATP production results in lactic acid accumulation, lowering muscle pH, impacting texture and water-holding capacity.
Rigor mortis ensues when ATP levels drop significantly, impeding muscle contracts.
pH drops during rigor mortis, with values ranging from 6.1-6.5 in cod, whereas some species might drop as low as 5.4.

Bacteriological Changes

Not covered directly but generally, postmortem spoilage often results from microbial activity, exacerbated by the initial autolytic changes.

Lipid Oxidation and Hydrolysis

Not detailed within the provided text but typically involves chemical reactions leading to spoilage in fish oils, affecting flavor and shelf life.

Nucleotide Degradation in Fish

Variability in nucleotide degradation patterns exists among fish species, notably in the levels of hypoxanthine (Hx).
Hx determination is not reliable for species like swordfish and redfish due to significant interspecies differences.

Autolysis in Fish Handling

Physical handling accelerates autolytic changes in chilled fish; sterile fillets show a higher breakdown rate of nucleotide catabolites compared to non-sterile whole gutted fish.
Crushing fish during storage can impact edibility and filleting yields, stressing the importance of proper handling practices.
Recommended storage: Iced fish should not be stacked in boxes deeper than 30 cm to minimize autolysis.

Proteolytic Enzymes and Autolysis

Autolytic changes include proteolysis which softens fish tissue, notably prevalent in fatty species like herring and capelin during summer feeding.
Autolysis enhances spoilage bacteria growth, reducing commercial value and affecting the nutritional quality of fish like capelin.
Studies showed that proteolytic enzymes can be inhibited by potato extracts, promoting preservation of nutritional value in fishmeal.

Cathepsins and Muscle Softening

Cathepsins, mainly cathepsins D and L, are acid proteases involved in autolytic degradation, being inactive in live tissues but active after physical damage or freezing.
Cathepsin L plays a significant role in softening salmon muscle and correlates well with muscle texture measurements.
Activity of cathepsins increases following freezing/thawing due to cell membrane breakdown, affecting softening rates.

Calpains in Fish Autolysis

Calpains, calcium-activated intracellular proteases, contribute to autolysis in fish muscle, though they’re primarily known for their role in mammal meat aging.
Active at physiological pH, calpains are implicated in the softening of fish during chilled storage and are specific to certain myofibrillar proteins.

Collagenases and Connective Tissue

Collagenase enzymes target connective tissue, leading to gaping or breakdown of muscle structure during prolonged storage.
Instrumental texture measurements decline as collagen, especially type V, is solubilized in chilled fish.

TMAO and Autolytic Changes

Trimethylamine oxide (TMAO) conversion to dimethylamine and formaldehyde by muscle enzymes can toughen fish muscle, impacting quality.
TMAO-demethylase activity is highest in gadoid fishes, particularly in dark muscle, emphasizing the importance of removing organ tissues to prevent toughening.

Prevention of Autolytic Effects

Optimal storage conditions are crucial for minimizing autolysis: keeping fish below -30°C and avoiding rough handling are key strategies.
Rough handling or physical damage are the most significant factors accelerating autolysis in fish products.

Postmortem Changes in Fish

Sensory Changes

Sensory changes involve appearance, odour, texture, and taste.
Rigor mortis is a significant postmortem change, initially resulting in a relaxed muscle that later becomes stiff.
Onset and resolution of rigor mortis vary by species and are influenced by factors like temperature and handling.
Higher temperatures can speed up rigor mortis, potentially causing gaping in fish like cod.
Fish with reduced glycogen due to starvation or stress experience quicker rigor onset.
Pre-rigor filleting allows for better texture; post-rigor fish becomes tough, while cooking pre-rigor yields softer texture.
Sensory evaluations of fish consider appearance, texture, and odour, with characteristic changes observable over time.
Fish stored on ice undergo a four-phase deterioration:
- Phase 1: Fresh with sweet taste, optimal 2-3 days post-catch.
- Phase 2: Neutral odour and taste, still pleasant texture.
- Phase 3: Signs of spoilage with unpleasant smells and altered texture.
- Phase 4: Spoiled and putrid characteristics.
Freshness evaluation scales assess sensory attributes based on EEC regulations.

Autolytic Changes

Autolysis, or "self-digestion," is crucial in fish spoilage, primarily divided into bacterial and enzymatic spoilage.
Lack of oxygen after death restricts energy production, leading to anaerobic metabolism.
Glycogen is the main energy source used for ATP production, which declines during rigor mortis.
The pH of muscle drops from around 6.8 to as low as 5.4-6.5 during postmortem, impacting texture and water-holding capacity.
Stress before capture decreases glycogen reserves, leading to differences in postmortem pH levels.
Muscles in rigor mortis lose moisture when cooked, leading to undesirable texture changes.
ATP degradation during rigor mortis contributes to texture and quality changes; rapid degradation affects perceived freshness.
Autolytic changes and nucleotide catabolism are crucial for assessing fish freshness, with specific ATP breakdown products used as indicators.
IMP is linked to desirable fresh fish flavour, while Hx contributes to bitter off-flavours in spoiled fish.
Freshness indices based on ATP breakdown may not always correlate with sensory quality due to variability among species.### Nucleotide Degradation Variability
Nucleotide degradation varies significantly between fish species, impacting the utility of Hx determination for certain species like swordfish and redfish.
Changes in nucleotide levels (IMP, Ino, Hx) occur differently in sterile and non-sterile cod fillets stored at 3°C.

Autolytic Changes

Physical handling accelerates autolytic changes in chilled fish; sterile fillets show faster breakdown of nucleotide catabolites compared to non-sterile gutted fish.
Crushing from ice or other fish adversely affects fish edibility and filleting yields, highlighting the role of autolytic processes in fish quality.
Iced fish storage capacity should not exceed 30 cm depth to minimize autolysis.

Proteolytic Enzymes

Proteases from fish muscle can lead to significant tissue softening, notably in fatty fish such as herring and capelin.
The phenomenon of belly-bursting in pelagic species is exacerbated during summer feeding on copepods and euphausiids.
Autolysis increases the risk of spoilage bacteria growth in bulk-stored fish, adversely affecting commercial value.
Presence of microbially produced biogenic amines lowers nutritive value.
Potato extracts can inhibit proteolysis and microbial growth, preserving nutritional quality.

Cathepsins

Cathepsins, acid proteases, are crucial in autolytic degradation after physical injury or freezing/thawing.
Cathepsin D is active at pH 3-8, while cathepsin L, more efficient at neutral pH, is associated with softening effects in salmon during spawning.

Calpains

Calpains are intracellular proteases involved in post-mortem muscle autolysis, tenderizing meat by digesting z-line proteins.
Fish calpains are more active in lower temperatures and affect muscle texture based on species-specific characteristics.
Both µ-calpain and m-calpain are active in fish muscle, with implications for commercial fish quality.

Collagenases

Collagenases target connective tissue in fish, leading to texture deterioration during storage.
Solubilization of type V collagen correlates with loss of fish texture, leading to gaping in fillets.
The hepatopancreas in prawns is thought to be the source of collagenase enzymes that contribute to texture softening.

Autolytic Changes During Frozen Storage

TMAO breakdown occurs through both bacterial action and specific enzymatic activity in fish, leading to dimethylamine (DMA) and formaldehyde (FA) production.
FA can cause toughening of muscle proteins, impacting quality negatively.
TMAO-ase, primarily found in gadoid fish, is responsible for tougher textures in frozen products.
It is essential to ensure gadoid minced fish is free of organ tissues to prevent toughening during storage.

Prevention of Autolytic Changes

Physical disruption of muscle cells is the leading cause of autolytic changes; minimizing rough handling can significantly enhance fish quality.
Recommended practices include avoiding temperature fluctuations during storage, preventing physical damage, and storing at temperatures below -30°C to inhibit enzyme activity.

Summary of Autolytic Changes in Chilled Fish

The effectiveness of preventing autolytic changes lies in understanding the roles of various enzymes and the impact of environmental conditions on fish quality.

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Description

Explore the fascinating changes that fish undergo postmortem, focusing on sensory, autolytic, bacteriological, and oxidative changes. Understand how these factors affect appearance, odour, texture, and taste during storage. Perfect for those studying fish biology and food science.